Seismic Response Mechanism And Analysis Method Of High-speed Railway Track Structure

Under the high-speed,high-load train loads and earthquakes,the track-subgradefoundation as a mutually structure may experience stiffness deterioration and excessive deformation,resulting in huge losses of human lives and property,and high maintenance costs.Therefore,it is crucial to carry out a systematic and thorough investigation of the seismic response mechanism of high-speed railway tracks.On the one hand,both moving train loads and the earthquakes have low frequency components,which means that lowfrequency resonances may occur in high-speed railways under the combined action of the two loads.On the other hand,in the seismic response analysis of multi-support structures with large span or crossing different sites,the non-uniform ground motion has attracted more and more researcher’s attention.However,the research on the dynamic response of the track-subgrade-foundation coupling system under the combined action of moving train loads and non-uniform ground motion is obviously insufficient.In this study,theoretical derivations and numerical simulations are used to thoroughly evaluate the dynamic response of the ballastless track-subgrade-foundation system under the coupling action of moving train load and non-uniform ground motion.The main research conclusions are summarized as follows:(1)The spatial variability of ground motion and the non-uniform ground motion synthesis method are summarized,and the non-uniform seismic acceleration satisfying the spatial effect is obtained by using the envelope function multiplied by the spatial stationary acceleration and iterating.In order to ensure that the power spectrum of the generated non-stationary seismic wave is consistent with the target power spectrum,the seismic wave is regenerated by combining the phase spectrum of the generated nonstationary seismic wave,and the spatial non-uniform ground motion whose energy in the frequency domain satisfies the target error is obtained by iteration.(2)The difference of seismic response of track-subgrade-foundation coupling system under uniform excitation and non-uniform excitation is studied by means of 3D finite element method.The acceleration time history,displacement time history,and transfer coefficients of seismic response of the track-subgrade-foundation system are studied in the time domain and frequency domain,respectively.The peak acceleration,peak displacement and their occurrence time of the track-subgrade-foundation system under non-uniform excitation are used to clarify the influence of the spatial effect of nonuniform ground motion on the dynamic response of high-speed railway track.The research shows that the spatial effect of ground motion is more obvious with the increase of the span of high-speed railway,and the spatial effect of ground motion should be considered in seismic design.(3)The differential equation of rail free vibration and the dynamic equilibrium equation of multi-layer beam system under uniaxial moving load are derived.Based on the Beijing-Shanghai high-speed railway track system and CRH3 high-speed train,a coupled ballastless track-subgrade finite/infinite element model under a moving train load is established,and the dynamic response law of the coupled system under a high-speed train is studied.The train load is simplified as a multi-axial surface load,which is added to the numerical model through the VDLOAD subroutine,and the model is verified by the finite-infinite element model(FE-IE)and the Euler-Bernoulli elastic beam(E-BEB).The results show that the relationship between ground vertical displacement and train speed is nonlinear,and the maximum amplitude of vibration occurs when the train speed reaches the “critical speed”.Through a large number of parameter analysis,it is revealed that the fastener with high elastic modulus and damping coefficient can reduce the vibration of track-subgrade system caused by moving load of high-speed train,and improving the stiffness of subgrade embankment is an effective way to alleviate the vibration of track-subgrade-foundation system.(4)The dynamic response of the track-subgrade-foundation system under the coupling of non-uniform ground motions and moving train loads is carried out based on the finite/infinite element model.The difference of dynamic response of the tracksubgrade-foundation coupling system under non-uniform excitation and uniform excitation is compared,which shows that the seismic spatial effects should be properly considered in the seismic analysis of high-speed railways.The peak displacement of highspeed railway track structure under spatial ground motion may appear earlier and induce greater damage.Compared with only under non-uniform ground motion excitation or only under train moving load,the dynamic response regularity of track slab and subgrade structure under coupling load is reduced,and the seismic influence is dominant,and the seismic action obviously increases the positive displacement of track slab.